Particulate filters are used in a wide variety of situations and systems in order to both capture material or retentate and to control the composition or characteristics of the output fluid. The ability to effectively remove particulate matter collected within filters allows for the extension of their usable life as well as the ability to reinstall and reuse the filters. This invention relates to a system and method for removing and collecting trapped matter or retentate from a filter.
Examples which illustrate the broad applicability of particulate filter cleaning systems include commercial and passenger diesel particulate filter systems, gasoline particulate filters, and industrial processes and applications where particulate matter or retentate from any effluent stream (solid, liquid, or gas) must be controlled or minimized.
One particular example involves particular filters, such as diesel or gasoline particulate filters, where retentate collects in the filter and must be periodically dislodged and removed. Any filter or retentate collection media or system, however, would be a candidate for automated cleaning with this method.
The particulate filter is used to reduce or eliminate certain undesirable particulate substances from the exhaust of diesel or gasoline powered vehicles or equipment and power systems. In this instance, soot and ash may build up within the filter. Soot, which is carbon-based, is periodically oxidized by means of a regeneration process whereby the temperature of the filter is raised in order to facilitate the reaction of soot with oxygen, nitrogen dioxide, or some other oxidizing agent. This allows the oxidized carbon-based soot to leave the filter as carbon-oxide byproducts. Ash, however, consists of incombustible material, largely metallic oxides, sulfates, phosphates, and other materials, which cannot be oxidized from the filter. The filter must be periodically removed from the engine, equipment or machinery and cleaned.
Currently, cleaning methods involve a combination of pressurized air, thermal cleaning, liquid-based washing, vibrations, and other related means. Specific to ceramic particulate filters, which are generally of a cellular honeycomb-type design, with a plurality of channels blocked at alternating ends, the most common cleaning method involves a combination of thermal cleaning and reverse-flow pressurized air. These systems generally consist of a nozzle, which traverses at a given height over the outlet surface of the filter. The nozzle blows pressurized air at the back face of the filter, which dislodges deposited ash, causing it to migrate to the front of the filter and fall out. Another permutation of pressurized air cleaning involves a pulsed flow bench whereby pressurized air is forced through the entire filter from the outlet face in an unsteady fashion.
While moderately successful, these methods have many disadvantages, which the present invention overcomes. In the case of the traversing nozzle, there is no seal created between the nozzle and the filter. Therefore air is not forced directly through the filter, but may instead take the path of least resistance. This path is oftentimes around the filter, or away from the filter, rather than through the clogged filter element or channels. In the case of the pulsed flow technique, an end cap is fitted to the outlet of the filter and pulsed air is forced through the entire filter at once. The effectiveness of this method is limited by the fact that, once again, the air will take the path of least resistance (away from the clogged regions). This results oftentimes in entire sections of the filter being left unaffected by the cleaning process.
A further limitation of available cleaning methods is a lack of in situ information to quantify the retentate levels in the filter (or degree of clogging) during and the cleaning process as well as the cleanliness of the filter after cleaning. Local clogs and defects are oftentimes invisible to the cleaning process. It is further desirable to ascertain the quantity or characteristics of the retentate inside the filter to optimize the cleaning process parameters to most efficiently clean the filter.
In situ knowledge of retentate levels or the extent of filter clogging also allows the cleaning processes to be terminated once the filter is clean, rather than for a predetermined amount of time, as is currently the case with most cleaning systems.
Another limitation of current pneumatic or air-flow cleaning techniques is the large energy and infrastructure requirements of the techniques. For example, a non-contact air nozzle or air knife approach may loose considerable amount of the air in the nozzle to the surroundings. In some examples these systems may operate at flow rates ranging from 20 scfm to 120 scfm or more and nozzle pressures of 100 to 150 psi or more. These systems require large and expensive air compressors, as well as air handling and conditioning systems. As these nozzle-based cleaning processes do not contact or seal against the filter, much of the high pressure air is deflected from the filter surface, flows around the filter, flows at low speeds through the filter in regions remote from the nozzle, or follows the path of least resistance through regions of the filter which may be clean or minimally clogged. Not only do these systems produce inferior results, but much of the air is also wasted in the process. The present invention creates a seal around the surface of the filter, directing high pressure air flow locally through clogged regions of the filter, thus producing superior results with lower system costs, infrastructure requirements, and less wasted energy.
Pulsed flow methods, which direct a pulse of high pressure compressed air through the entire filter volume reduce air losses from escaping the filter, but also require large and expensive air compressors and infrastructure. The high pressure also may present a safety hazard and produce loud, undesirable “explosive” sounds. The sudden burst of high pressure pulses also introduces additional risk for retentate leakage and escape to the work environment, which presents a health and safety hazard. Furthermore, although the maximum pressure and flow rates of these systems may be high, the local flow through the individual channels is low (given the large filter area subjected to the flow) and also follows the path of least resistance. Similar to the air nozzle approach, pulsed cleaners also suffer from incomplete and inefficient retentate removal from the filter.
Alternative cleaning approaches, such as wet cleaning methods with chemical solutions, water, or even ultra-sonic cleaning, using a liquid to couple the ultrasonic waves to the filter, are also used. These cleaning methods suffer from limitations including chemical incompatibilities with certain filter media, or incompatibility with specific filter components (such as the fibrous matting in the case of certain types of particulate filters, for example). Additional limitations of wet cleaning systems include additional steps to dry or remove the cleaning liquid or solution from the filter following cleaning, as well as the recycling or disposal of the fluid itself.
The above-listed examples highlight the need for an improved process of dislodging and removing particulate matter or retentate collected on or in the filter media, which will have considerable utility for a broad range of applications and fields of uses.
The filter retentate cleaning system and method described in this disclosure enables direct and highly-localized, forced air cleaning of filters to efficiently remove the collected retentate media. It also allows for the cleanliness of the filter or retentate media to be quantified, on a local level and in the aggregate, before, during, or after the cleaning process.